Jarring tool

ABSTRACT

A jarring tool in accordance with this invention may jar in either upward or downward direction and operates in either direction without rotation or the like. A jarring tool of the present invention comprises an elongated outer member with an elongated inner member telescopically mounted therein. Each of the members has a pair of axially directed striking surfaces facing in opposite directions, and each such surface of one member is opposite to and engageable with one of the striking surfaces of the other member. The distance between the striking surfaces on one of the members is greater than the distance between the striking surfaces on the other member, so as to allow telescopic movement between the two members limited in either direction by engagement of two of the opposed striking surfaces. Spline means cooperative between the two members prevent rotation but allow relative axial movement. Latching means hold the two members in neutral relative positions. The latching means is releasable under axial forces of sufficient magnitude imposed on the members in one direction to allow telescopic contraction of the members and striking of one set of opposed striking surfaces, and releasable under axial forces of sufficient magnitude imposed on the members in the other direction to allow telescopic extension of the members and striking of the other set of striking surfaces.

United States Patent n91 Bottoms JARRING TOOL [75] Inventor: Clifford C. Bottoms, San Fernando,

Calif.

[73] Assignee: Dresser Industries, Inc., Dallas, Tex. [22] Filed: Mar. 12, 1973 [21] Appl. No.: 340,349

[52] US. Cl. 175/304, 166/178 [51] Int. Cl E2lb 1/10 [58] Field of Search 166/178; 175/293, 299,

[56] References Cited UNITED STATES PATENTS 2,008,743 7/1935 Black 175/304 2,247,560 7/1941 Phipps 175/304 X 3,203,482 8/1965 Lyles 175/299 3,345,832 10/1967 Bottoms... 175/321 X 3,575,246 4/1971 Jones 175/293 3,685,598 8/1972 Nutter 175/304X 3,233,690 2/1966 lsawrence 175/302x Primary Examiner-David H. Brown Attorney, Agent, or F irm-Browning & Bushman [57] ABSTRACT A jarring tool in accordance with this invention may [11] 3,834,471 1 Sept. 10, 1974 face of one member is opposite to and engageable with one of the striking surfaces of the other member. The distance between the striking surfaces on one of the members is greater than the distance between the striking telescop surfaces on the other member, so as to allow ic movement between the two members limited in either direction by engagement of two of the opposed striking surfaces. Spline means cooperative between the two members prevent rotation but allow relative axial movement. Latching means hold the two members in neutral relative positions. The latching means is releasable under axial forces of sufficient magnitude imposed on the members in one direction to allow telescopic contraction of the members and striking of one set of opposed striking surfaces, and

releasable under axial forces of sufficient magnitude imposed on the members in the other direction to allow telescopic extension of the members and striking of the other set of striking surfaces.

15 Claims, 5 Drawing Figures PATENIED SEP 1 0 I974 SIEHUI 2 FIG] JARRING TOOL BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a well known type of tool known as a jarring tool or sometimes simply as a jar." Jars are used in connection with drilling equipment to deliver hard blows to articles which are stuck in a hole so as to free such articles. In many cases, jars are used for what are known as fishing operations. In these cases an article, such as a piece of drilling equipemnt, known as the fish may be lost in a hole which has been drilled. To retrieve the article a gripping tool is lowered into the hole and attached to the article. A jar may be disposed in the drill string above the gripping tool and may be used to dislodge the article if it is stuck in the hole.

In other instances a jar may be disposed in a drill string near the drill bit during actual drilling of the hole so that it can be used to free the bit, should it become stuck.

2. Description of the Prior Art Jarring tools can generally be divided into several classes according to their mode of operation. Some types must be rotated to effect the jarring action and are thus incapable of transmitting torque.

Another type of jar, shown for example in U.S. Pat. No. 3,233,690, depends upon relative rotation of its inner and outer members to allow the jarring action to occur even though suchrotation is actuated by a straight axial force. While such tools have, in the past, provided the advantage of being able to jar either upwardly or downwardly, their dependence upon relative rotation of the members has limited their torque transmitting capabilities. The device of U.S. Pat. No. 3,233,690, for example is capable of transmitting only a limited amount of torque when rotated in one direction. When rotated in the other direction, it becomes a slack joint so that it is no longer operative as a jar even though it may again be capable of transmitting some limited amount of torque.

In still another type of jar; e.g. U.S. Pat. No. 2,733,046, U.S. Pat. No. 1,801,673, and U.S. Pat. No. 1,989,906; the inner and outer members are firmly secured against relative rotation, as by spline means, the jarring being effected by a straight pull on the drill string. Such jars can transmit large amounts of torque but have in the past been limited to jarring in only one direction. U.S. Pat. No. 3,203,482 shows a jar of this general type which can be assembled to jar either upwardly or downwardly. However, once assembled, and thus when in use downhole, it can only jar in one direction.

SUMMARY OF THE INVENTION The present invention provides a straight pull or push jar which is capable of transmitting large amounts of torque, and of jarring either upwardly or downwardly. The jar comprises two elongated, telescopically mounted members each having a pair of axially directed striking surfaces facing in opposite directions. Each such surface on one member is opposed to and engageable with one of the surfaces of the other member. The distance between the pair of surfaces on one member differs from the distance between the pair on the other member so as to allow telescopic movement between the two members limited in either direction by engagement of a set of opposed striking surfaces. The members are splined, preferably with a plurality of ball bearing splines to permit relative axial movement, but prevent relative rotation therebetween.

Latching means maintain the two members in neutral axial positions with respect to each other under axial forces below a particular magnitude. Axial forces above this magnitude imposed on the members in one direction cause release of the latching means permitting telescopic contraction of the members and striking of one set of opposed striking surfaces. Axial forces imposed in the other direction cause release of the latching means permitting telescopic extension and striking of the other set of surfaces.

The latching means preferably comprise a plurality of radially resiliently biased ball or sphere detent elements on the outer member and mating indentations on the inner member. The ball detents and biasing means are removable from the outside of the tool so that the force necessary for release can be easily varied by varying the number of detent elements. The latching and spline means as well as the striking surfaces preferably operate in a lubricant which can be sealed off by means of a pair of annular seals disposed between the two members at opposite ends of the portions along which the spline means and latching means are located.

It is therefore an object of the present invention to provide a straight-pull-push, high torque transmitting, bidirectional jarring tool.

It is a further object of the invention to provide a straight-pull-push, high torque transmitting jar having latching means for holding the members of the jar in neutral relative positions.

Still another object of the invention is the provision in a jar of radially resiliently biased latching means releasable under forces acting in either axial direction.

Another object of the present invention is to provide, in a jar, a plurality of latching means whose number can be easily varied to vary the force necessary for release thereof.

Still another object of the present invention is the provision of improved spline means in a straight-pullpush jar.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the invention will be made clear by the following detailed description and the drawings wherein:

FIG. 1 is a longitudinal view of a jar according to the invention, partly in section and partly in elevation, in neutral position;

FIG. 2 is a view similar to that of FIG. 1 showing the jar as it delivers an upward blow;

FIG. 3 is a view similar to that of FIG. 1 showing the jar as it delivers a downward blow;

FIG. 4 is a transverse cross section along lines 4-4 of FIG. 1 on a larger scale;

FIG. 5 is a broken away detail veiw of a portion of the interior of the outer member in the area of the spline and latching means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the jarring tool, indicated generally by the letter J comprises two elongated members 2 and 4. The outer member 2 has a longitudinal bore 6 therethrough in which inner member 4 is telescopically mounted. lnner member 4 has a longitudinal passageway 8 therethrough to allow drilling mud to flow through the tool. To facilitate assembly of the tool, each of the members 2 and 4 is comprised of a plurality of sections. Outer member 2 comprises upper packer sub 10, spline sub 12, and lower packer sub 14 which are joined end to end by means of suitable threaded connections 16 and 18. Outer member 2 has first and second ends 20 and 22 respectively. As the jar is shown in the drawings, first end 20 is the upper end and second end 22 is the lower end of member 2. However it will be readily appreciated that the orientation of the tool could be reversed without departing from the spirit of the invention.

Inner member 4 is comprised of an upper wash pipe 24, spline section 26,and connector sub 28 joined end to end'by threaded connections 30 and 32. A conventional annular o-ring seal 33 is provided between spline section 26 and connector sub 28.

Inner member 4 is telescopically mounted in the bore 6 of outer member 2 with its first or upper end 44 in the bore 6 axially inboard of end 20 of outer member 2 and its second or lower end 46 free of the bore 6 and axially outboard of end 22 of outer member 2.

Spline section 26 has a flange portion 34 of greater outer diameter than the remainder of spline section 26.

The axially directed shoulder 36 between flange 34 and the remainder of spline section 26 serves as one of a pair of striking surfaces on inner member 4. The other striking surface is provided by the axially directed shoulder 37 on the upper end of flange 34. The striking surfaces 36 and 37 of inner member 4 face in opposite directions.

Outer member 2 has an internal shoulder 40 opposed to and engageable with shoulder 36. The bottom of upper packer sub 10 forms a shoulder 43 opposed to and engageable with shoulder 37. Shoulders 40 and 43 on outer member 2 are a pair of axially directed striking surfaces which face in opposite directionsThe distance between shoulders 36 and 37 on the inner member 4 is less than the distance between shoulders 40 and 43 on the outer member 2 so that telescopic movement between members 2 and 4 is permitted. Shoulders 36 and 40 form a set of striking surfaces which limit relative axial movement between members 2 and 4 in one direction, i.e. they limit extension of the members (see FIG. 2), and shoulders 37 and 43 form a set of striking surfaces which limit relative axial movement in the other direction, i.e. they limit contraction of the members (see FIG. 3).

Cooperative between members 2 and 4 for preventing relative rotation while allowing relative axial movement are a plurality of ball bearing spline means. The spline means comprise a plurality of longitudinally extending preferably arcuate grooves 48 in the outer surface of spline section 26. An equal number of similar longitudinally extending also preferably arcuate grooves 50 in the inner surface of spline sub 12 are arranged so that each groove 50 is circumferentially aligned with one of the grooves 48. Disposed between each set of grooves 48, 50 is a set of ball bearings 52.

Located between each two grooves 48 in spline section 12 are a plurality of axially and circumferentially offset indentations 54 each having the configuration of a spherical segment whose depth is less than the spherical radius. A detent element in the form of a metal sphere is biased radially inwardly into each indentation 54 by a helical compression spring 58. Each spring 58 is mounted on a plug 60 which is screwed into a radial bore 62 in the outer member 2. A hex wrench socket 64 is provided in each plug 60 so that it can be removed from the exterior of the jar J. The bores 62 are disposed so as to register with indentations 54 when the jar is in a neutral position, i.e., a position in which the striking surfaces of each mating set are separated and the tool can be activated to cause striking of either set as shown in FIG. 1.

The latching means comprised of indentations 54, spheres 56, and springs 58 hold the members 2 and 4 in the neutral axial position under forces below a particular magnitude, say X, which may be chosen by the user, e.'g. it might be a value greater than the forces encountered during ordinary drilling but less than that which would cause damage to the drilling apparatus. The end of each spring 58 which is adjacent its respective sphere detent element 56 forms a seat on which the sphere may freely rotate. Thus when a force greater than X is applied axially to the members 2, 4, the springs 58 will be compressed allowing spheres 56 to roll out of the indentations 54 and along the spline section 26 within their spring seats. The latching means are circumferentially and axially offset to distribute their force. The circumferential offsetting also prevents a sphere from becoming accidentally lodged in the wrong indentation during the relative axial movement of the members and thus interfering with the jarring action.

The magnitude of the force which is needed to release the latching means can be adjusted by proper choice of spring strength, etc., but also by the number of detent elements used. If each of the radial bores 62 has a detent member mounted therein, X will be relatively high. To decrease X, a suitable number of the detent carrying plugs 60 can be removed and replaced by plain plugs. Thus one jar can be adapted to different situations in a simple manner, on the job, without disassembly of the tool.

Each of the packer subs 10 and 14 carry an annular seal 66 which seals between the inner and outer members. The seal 66 of upper packer sub 10 is retained by an annular packer nut 68. The spline means, latching means, and striking surfaces, which operate between members 2 and 4, are located along axially inner portions of members 2 and 4 so that they are always within the bore 6 of outer member 2. Thus the seals 66 can be disposed axially outboard of the spline means, striking surfaces, and latching means to form a lubricant chamber to retain a lubricant therearound. The inner diameters of the packer subs are sized so as to fit closedly around the appropriate parts of member 4 and thus help stabilize the tool.

The end 20 of outer member 2 is provided with female thread 70 for connection to a drill stem or other member above the jarring tool. End 46 of inner member 4 is provided with male thread 72 for connection to a drill stem or other member below the jarring tool. The tool would preferably be disposed in a drill string close to its lower end, i.e., to the bit or fish.

Because of its high torque transmitting capabilities, the jarring tool of the invention can be used in drilling as well as fishing and in many applications unsuitable for the relatively rotating prior art jar. At the same time it can be used to jar either upwardlyor downwardly from its neutral position.

FIG. 1 shows the jar in its neutral position as it would appear during ordinary drilling or fishing. If the drill bit (in drilling) or fish (in fishing) is stuck, the operator might release the counter balancing means sufficiently to allow the weight of the drill to impose the downward, i.e. compressive, force. When this force finally exceeds the value X for the tool, as assembled with a given number of detent elements, the latching means would be released, and the rapid expansion of the string above the tool would cause outer member 2 to move rapidly downwardly so that the tool would telescopically contract, shoulder 43 delivering a blow to shoulder 37 and thus to the stuck fish or bit connected to inner member 4 (see FIG. 3). The operator could then raise the upper string to return member 2 to neutral postion and deliver another blow either upwardly or downwardly. Note (in FIG. 3) that the tool is designed so that there is a slight clearance between upper surface 38 of connector sub 28 and the lower edge 42 of lower packer sub 14 when shoulders 43 and 38 are engaged so that shoulder 37 recieves the full force of the blow.

To deliver an upward blow the procedure is reversed. The operator would pull up on the drill string putting an axial tensile force on the entire string including members 2 and 4. When this force exceeded X the latching means would release and the contraction of the upper portion of the string would cause member 2 to move upwardly telescopically extending the tool and striking shoulder 40 against shoulder 36 as shown in FIG. 2.

The invention having been thus described in detail, what is claimed is:

l. A jarring tool comprising:

an elongated outer member having a longitudinal bore therethrough and including a first end, a second end, and first and second axially directed striking surfaces, said striking surfaces being disposed in opposite directions;

an elongated inner member telescopically mounted in the bore of said outer member and including a first end, a second end, a first axially directed striking surface opposed to and engageable with said first striking surface of said outer member and a second axially directed striking surface opposed to and engageable with said second striking surface of said outer member, the distance between the striking surfaces on said inner member being different from the distance between the striking surfaces on said outer member;

longitudinally extending spline means cooperative between said outer member and said inner member for preventing relative rotation between said outer member and said inner member while allowing relative longitudinal movement between said outer member and said inner member; and

latching means cooperative between said outer member and said inner member for maintaining said outer member in a neutral axial position with respect to said inner member under axial forces on said members below a particular magnitude, reasonable from said neutral axial position under forces in excess of said magnitude imposed on said members in one axial direction to allow telescopic contraction of said members bringing said first striking surfaces into engagement with each other,

and releasable from said neutral axial position under forces in excess of said magnitude imposed on said members in the other axial direction to allow telescopic extension of said members bringing said second striking surfaces into engagement with each other;

wherein one of said members has a radially directed indentation therein, and said latchingmeans comprises a detent element carried by the other of said members and means radially resiliently biasing said detent element into said indentation.

2. A jarring tool according to claim 1 wherein said spline means comprises a longitudinally extending groove in the outer surface of said inner member intermediate the ends of said inner member, a longitudinally extending groove in the bore of said outer member opposite the groove in the inner member, and a plurality of rolling bearings between said grooves.

3. A jarring tool according to calim 1 wherein said spline means and said latching means are located along axially inner portions of said members, within the bore of said outer member, said tool further comprising a pair of annular seals disposed between said inner member and said outer member axially outboard of and at opposite ends of said axially inner portions to form a lubricant chamber for retaining a lubricant on said portions.

4. A jarring tool according to claim 1 wherein said inner member has a longitudinal passageway therethrough and wherein the first end of said inner member is located in the bore of said outer member axially inwardly of the first end of said outer member and the second end of said inner member is free of the bore of said outer member axially outwardly of the second end of said outer member, said first end of said outer member and said second end of said inner member each including attachment means for attachment to pieces of drilling equipment.

5. A jarring tool according to claim 1 wherein said striking surfaces are located along axially inner portions of said members within the bore of said outer member, said tool further comprising a pair of annular seals disposed between said inner member and said outer member axially outboard of and at opposite ends of said axially inner portions to form a lubricant chamber for retaining a lubricant on said portions.

6. A jarring tool according to claim 5 wherein said inner member further comprises an annular flange portion extending circumferentially around said inner member, said flange portion having opposite axially directed ends which define the first and second striking surfaces of said inner member, wherein the first and second striking surfaces of said outer member are defined by inwardly directed shoulders on the inner surface of said outer member, said shoulders being at opposite ends of said flange portion and spaced apart a greater distance than the ends of said flange portion.

7. A jarring tool according to claim 1 wherein said indentation has the configuration of a spherical segment, wherein said other of said members has a radial hole therein and said biasing means is mounted in said hole, and wherein said detent element is a rigid sphere carried by and freely rotatable on a seat on one end of said biasing means.

8. A jarring tool according to claim 7 wherein said biasing means is a helical compression spring and said seat is comprised of one end of said spring.

9. A jarring tool according to claim 7 wherein said one of said members is the inner member and said other of said members is the outer member.

10. A jarring tool according to claim wherein said radial hole extends through a wall of said outer member and said biasing means is mounted on a plug removably secured within said radial hole.

11. A jarring tool according to claim 7 comprising a plurality of such spheres carried by an equal number of such biasing means each mounted on one of a plurality of such radial holes, said radial holes being circumferentially offset from one another on said other of said members, and wherein said one of said members has a plurality of said indentations each of which is in register with one of said spheres when said outer member is in said neutral position relative to said inner member.

12. A jarring tool according to claim 11 wherein said radial holes are axially offset from one another.

13. A jarring tool comprising:

an elongated outer member having a longitudinal bore therethrough and including an axially directed striking surface;

an elongated inner member telescopically mounted in the bore of said outer member and including an axially directed striking surface opposed to and engageable with said striking surface of said outer member;

longitudinally extending spline means cooperative between said outer member and said inner member for preventing relative rotation between said outer member and said inner member while allowing rel ative longitudinal movement between said outer member and said inner member; and

latching means cooperative between said outer mem her and said inner member for maintaining said outer member in an axial position with respect to said inner member in which said striking surfaces are separated under axial forces below a particular magnitude, and releasable from said position under an axial force in excess of said magnitude imposed on said members in one axial direction to allow telescopic movement of said members bringing said striking surfaces into engagement with each other; I

and wherein one of said members has a radially directed indentation therein, and said latching means comprises a detent element carried by the other of said members and means radially resiliently biasing said detent element into said indentation.

14. A jarring tool according to claim 13 wherein said indentation has the configuration of a spherical segment, wherein said other of said members has a radial hole therein and said biasing means is mounted in said hole, and wherein said detent element is a rigid sphere carried by andfreely rotatable on a seat on one end of said biasing means.

15. A jarring device according to claim 14 wherein said one of said members is the inner member and said other of said members is the outer member, and comprising a plurality of such spheres carried by an equal number of such biasing means, said outer member having a plurality of such radial holes circumferentially offset from one another and each extending through a wall of said outer member, each of said biasing means being mounted on a plug removably secured within one of said radial holes, and wherein said inner member has a plurality of said indentations each of which is in register with one of said spheres when said outer member is in said position relative to said inner member.

d UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 383M471 Dated September 10, 197M Inventor(s) Clifford C. Bottoms It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, claim 1, lines 62 and 63, the word "reasonable" should read -releasable-.

Column 6, claim 6, line 7, the numeral T95" should read +-l--.

Column 7, claim 10, line H, the numeral "5" should read --9-.

Column 7;*e1eim 11, line 10, the word "on" should read in--.

Signed and sealed this 21st day of January 1975.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM uscoMM-oc 80376-P69 ".5. GOVERNMENT PRINTING OFFICE I969 O-365-33l. 

1. A jarring tool comprising: an elongated outer member having a longitudinal bore therethrough and including a first end, a second end, and first and second axially directed striking surfaces, said striking surfaces being disposed in opposite directions; an elongated inner member telescopically mounted in the bore of said outer member and including a first end, a second end, a first axially directed striking surface opposed to and engageable with said first striking surface of said outer member and a second axially directed striking surface opposed to and engageable with said second striking surface of said outer member, the distance between the striking surfaces on said inner member being different from the distance between the striking surfaces on said outer member; longitudinally extending spline means cooperative between said outer member and said inner member for preventing relative rotation between said outer member and said inner member while allowing relative longitudinal movement between said outer member and said inner member; and latching means cooperative between said outer member and said inner member for maintaining said outer member in a neutral axial position with respect to said inner member under axial forces on said members below a particular magnitude, reasonable from said neutral axial position under forces in excess of said magnitude imposed on said members in one axial direction to allow telescopic contraction of said members bringing said first striking surfaces into engagement with each other, and releasable from said neutral axial position under forces in excess of said magnitude imposed on said members in the other axial direction to allow telescopic extension of said members bringing said second striking surfaces into engagement with each other; wherein one of said members has a radially directed indentation therein, and said latching means comprises a detent element carried by the other of said members and means radially resiliently biasing said detent element into said indentation.
 2. A jarring tool according to claim 1 wherein said spline means comprises a longitudinally extending groove in the outer surface of said inner member intermediate the ends of said inner member, a longitudinally extending groove in the bore of said outer member opposite the groove in the inner member, and a plurality of rolling bearings between said grooves.
 3. A jarring tool according to calim 1 wherein said spline means and said latching means are located along axially inner portions of said members, within the bore of said outer member, said tool further comprising a pair of annular seals disposed between said inner member and said outer member axially outboard of and at opposite ends of said axially inner portions to form a lubricant chamber for retaining a lubricant on said portions.
 4. A jarring tool according to claim 1 wheRein said inner member has a longitudinal passageway therethrough and wherein the first end of said inner member is located in the bore of said outer member axially inwardly of the first end of said outer member and the second end of said inner member is free of the bore of said outer member axially outwardly of the second end of said outer member, said first end of said outer member and said second end of said inner member each including attachment means for attachment to pieces of drilling equipment.
 5. A jarring tool according to claim 1 wherein said striking surfaces are located along axially inner portions of said members within the bore of said outer member, said tool further comprising a pair of annular seals disposed between said inner member and said outer member axially outboard of and at opposite ends of said axially inner portions to form a lubricant chamber for retaining a lubricant on said portions.
 6. A jarring tool according to claim 5 wherein said inner member further comprises an annular flange portion extending circumferentially around said inner member, said flange portion having opposite axially directed ends which define the first and second striking surfaces of said inner member, wherein the first and second striking surfaces of said outer member are defined by inwardly directed shoulders on the inner surface of said outer member, said shoulders being at opposite ends of said flange portion and spaced apart a greater distance than the ends of said flange portion.
 7. A jarring tool according to claim 1 wherein said indentation has the configuration of a spherical segment, wherein said other of said members has a radial hole therein and said biasing means is mounted in said hole, and wherein said detent element is a rigid sphere carried by and freely rotatable on a seat on one end of said biasing means.
 8. A jarring tool according to claim 7 wherein said biasing means is a helical compression spring and said seat is comprised of one end of said spring.
 9. A jarring tool according to claim 7 wherein said one of said members is the inner member and said other of said members is the outer member.
 10. A jarring tool according to claim 5 wherein said radial hole extends through a wall of said outer member and said biasing means is mounted on a plug removably secured within said radial hole.
 11. A jarring tool according to claim 7 comprising a plurality of such spheres carried by an equal number of such biasing means each mounted on one of a plurality of such radial holes, said radial holes being circumferentially offset from one another on said other of said members, and wherein said one of said members has a plurality of said indentations each of which is in register with one of said spheres when said outer member is in said neutral position relative to said inner member.
 12. A jarring tool according to claim 11 wherein said radial holes are axially offset from one another.
 13. A jarring tool comprising: an elongated outer member having a longitudinal bore therethrough and including an axially directed striking surface; an elongated inner member telescopically mounted in the bore of said outer member and including an axially directed striking surface opposed to and engageable with said striking surface of said outer member; longitudinally extending spline means cooperative between said outer member and said inner member for preventing relative rotation between said outer member and said inner member while allowing relative longitudinal movement between said outer member and said inner member; and latching means cooperative between said outer member and said inner member for maintaining said outer member in an axial position with respect to said inner member in which said striking surfaces are separated under axial forces below a particular magnitude, and releasable from said position under an axial force in excess of said magnitude imposed on said members in one axial direction to allow telescopic movemenT of said members bringing said striking surfaces into engagement with each other; and wherein one of said members has a radially directed indentation therein, and said latching means comprises a detent element carried by the other of said members and means radially resiliently biasing said detent element into said indentation.
 14. A jarring tool according to claim 13 wherein said indentation has the configuration of a spherical segment, wherein said other of said members has a radial hole therein and said biasing means is mounted in said hole, and wherein said detent element is a rigid sphere carried by and freely rotatable on a seat on one end of said biasing means.
 15. A jarring device according to claim 14 wherein said one of said members is the inner member and said other of said members is the outer member, and comprising a plurality of such spheres carried by an equal number of such biasing means, said outer member having a plurality of such radial holes circumferentially offset from one another and each extending through a wall of said outer member, each of said biasing means being mounted on a plug removably secured within one of said radial holes, and wherein said inner member has a plurality of said indentations each of which is in register with one of said spheres when said outer member is in said position relative to said inner member. 